140 Bulletin, Vanderbilt Marine Museum, Vol. IV 



suitable hole, just as the hermit crab finds a shell? This problem is 

 one well worth investigation by field workers. 



Life history : Critical investigation of the life history of E. lucun- 

 ter (Linne) has been reported by Dr. Th. Mortensen, who reared 

 the species at Tobago, B. W. I. (Studies of the Development and 

 Larval Forms of Echinoderms, p. 71, pi. I, figs. 1-2, pi. XII, fig. 1, 

 1921, Copenhagen.) 



Technical description : Agassiz states that there is such variation 

 within this species, in the proportion of the test, the structure of the 

 ambulacra near the actinostome, more or less petaloid, and in the 

 proportions of the spines and test, that only by examination of a large 

 series of specimens, that the few good specific characters of E. lucun- 

 ter may be determined. The test is thin, elongated, the poriferous 

 zone broad, the pore pairs arranged in arcs of seven or eight, some- 

 times only six, the pores of pair large, distant; the auricles of very 

 great size, extending in a T-shaped, broad column half way the 

 length of the polar axis, connected by a stout ridge at base, equalling 

 in height one-third of the auricles. The auricular arch is small. The 

 actinostome is large, pentagonal; in young specimens the number of 

 coronal plates of ambulacra is materially greater than in the inter- 

 ambulacra but older specimens show little difference in the size of the 

 primary tubercles of the two areas. In very large old specimens as 

 the test becomes more gibbous, the size of the coronal plates greatly 

 increases and the primary vertical rows of tubercles frequently 

 attain an astonishing size, and are sometimes flattened which has 

 caused such specimens to be confused with true Stomopneustes. 



The primary spines are stout, conical, finely striated longitudinally. 

 The secondary spines are very fine, fragile, of similar design as the 

 primaries but less than one-fourth as long. 



There are numerous clusters of small, gemmiform pedicellariae 

 encircling the actinostome. These each have a long, slender stem and 

 a head composed of three rounded triangulate valves, the distal mar- 

 gins of which are distinctly dentate. These are also moderately 

 abundant, more scattered among the secondary spines and such iso- 

 lated gemmiform pedicellariae are frequently substantially larger 

 than those on the actinostome, and each valve has a distinct hook 

 at the tip. (Figs. A and B.) 



The large, tridactyl pedicellariae are less abundant on the actino- 

 stome than the gemmiform, but are present in goodly numbers. Each 

 has a long, slender stem, the neck of which is flexible, the head much 



